A purple and/or orange Golden Nugget. I heard they were the rarest of the Golden Nuggets and with some extra cash lying around I'll know what to look for on ebay
I'm not sure which of the decks are classed as "very rare", but here is a scan of all of the Golden Nugget designs as we know them best. I imagine the one you're referring to is on the upper-right corner of the picture.
Don't worry, lol, those are scans I found on an old website (although it's now unfortunately down). It had a lot of information and scans about various cards, it was very useful. If I find it, and it again becomes available, I will post the link up here.